An engine for an automobile generates power by mixing fuel with air introduced from the outside at an appropriate ratio and combusting the mixture.
In order to obtain a desired output and combustion efficiency, it is necessary to supply a sufficient amount of outside air for combustion during a process of generating power by operating the engine. To this end, a turbocharger is used as an apparatus that supercharges the engine with air for combustion in order to improve a combustion efficiency of the engine.
In general, the turbocharger is an apparatus that increases output of the engine by rotating a turbine by using pressure of exhaust gas discharged from the engine and then supplying high-pressure air into a combustion chamber by using a rotational force of the turbine. The turbocharger is applied to most diesel engines, and recently, the turbocharger is also applied to gasoline engines.
In addition, nitrogen oxide (NOx) included in exhaust gas is considered an air pollutant, and research is being conducted to reduce emissions of NOx.
An exhaust gas recirculation (EGR) system is a system mounted in a vehicle in order to reduce various exhaust gas particles. In general, NOx increases in a case in which a proportion of air in the gaseous mixture is large and thus combustion is smoothly carried out. Therefore, the exhaust gas recirculation system is a system that mixes a part (e.g., 5 to 20%) of exhaust gas discharged from the engine with the gaseous mixture again so as to reduce the amount of oxygen in the gaseous mixture and hinder the combustion, thereby inhibiting generation of NOx.
An exhaust gas recirculation (EGR) system for a gasoline engine is mounted in the vehicle in order to improve fuel economy. With the exhaust gas recirculation (EGR) system, it is possible to improve fuel economy by advancing the ignition timing by reducing a pumping loss within a low-speed/low-load region and reducing a temperature in the combustion chamber within a medium-speed/medium-load region.
In a given exhaust gas recirculation system, there is a low pressure exhaust gas recirculation (LP-EGR) apparatus. The LP-EGR apparatus recirculates exhaust gas which has passed through the turbine of the turbocharger into an intake passageway at a front end of a compressor.
In the case of the exhaust gas recirculation system in the related art, recirculation gas is supplied to the combustion chamber of the engine by a rotational force of the turbine and the compressor while the turbocharger operates.
However, when the turbocharger does not operate, negative pressure may be generated at the front end of the compressor, and as a result, a separate differential pressure generating valve is used. However, in a case in which the differential pressure generating valve is mounted as described above, there is a problem in that manufacturing costs of the vehicle are increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.